notable to logon

My system OS is windows2000professional,when i boot my system it is coming up to welcome screen ok.then iam giving my username,password and domain,when i say enter,again it is coming back to welcomescreen(ctrl+alt+del).erlier it was working fine,i tried with administrator account also, still same problem is persisting.
i also tried with pagefile.sys(deleted this file and restarted the system)still same problem.
kindly advise me if any suggestions i will be thankfull to you.